The way filesystems work, a directory is not actually a folder containing files but rather a directory is a file that contains inode pointers to “child” files connected to it. Meaning, from a file system perspective, a file is a file, but a directory is just a file containing list of connected files.
So from the command line perspective, doing this:
cp dir1 copyDir1
Would basically mean copy the file named, dir1
to a new file named copyDir1
. And as far as the file system is concerned, dir1
is just a file anyway; the fact it’s a “directory” will only be apparent when the filesystem actually checks dir1
to see what that pile of bits actually is.
The -r
flag tells the file system to recursively roll down the file/directory tree and copy any & all contents that might be a “child” of that file to a new place.
Now as to why that might seem superfluous or redundant, this really comes down to historic methods of dealing with file systems. As well as creating a system that is safe from all types of user related errors; accidental as well as intentional.
Meaning, let’s say you have a ~/bin
file in your home directory you want to copy but accidentally left out the ~
—because you are a human and make mistakes—so its just /bin
like this:
cp /bin/ ~/copy_of_bin
With the “safety net” of /bin
being a directory combined with the need for the -r
flag you will avoid accidentally copying the whole binary root of the system you are on into your home directory. If that safety net did not exist, a minor—or possibly major—disaster would happen.
The logic here being that in the days pre-GUI (graphical user interfaces) logical/behavioral conventions need to be set to avoid having user created mishaps that can potentially kill a system. And using the -r
flag is now one of them.
If that seems superfluous, then need look no further than modern GUI system one can place above Linux file systems. A GUI addresses basic user issues like this by allowing one to drag and drop files and directories with ease.
But in the case of the realm of text-based interfaces, lots of the “user experience” within that world is basically just logical and hueristic-based road bumps that help keep the user in check so potential disaster can be averted.
Similarly this is why Linux/Unix filesystems don’t have 777
permissions and sudo
rights set by default and how real system administrators wince when a user sets 777
permissions or grants everyone sudo
rights. These are the basic things one does to ensure the system is stable and as “user proof” as possible; anyone rushing to short-circuit those conventions will most likely cause damage to their system without even knowing it.
Additional Info: Another answer here on the Unix Stack Exchange site gives a good explanation of why a non-recursive copy of a directory is problematic; emphasis is mine.
Well, without the -R flag, it's only possible to copy files, because it's rather unusual that someone wants to non-recursively copy a directory: A non-recursive copy would just result in a second name for the directory, pointing to directly the same directory structure. Because that's rarely what people want, and there is actually a separate program that does this (ln), a non-recursive copy of directories is not allowed.
So if a directory is just really a file with inode items inside of it, making a straight copy of that file would just be the equivalent of how a hard link would work. Which is not what anyone wants.
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